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On Sun, Feb 14, 2021 at 12:25 PM, Ed Krome wrote:

Thank you to all who replied. But, since the values I was seeing didn't match
prescribed values (and it was driving me a bit nuts), I tried the experimental
approach. I took a single RF Demo Kit board with the same cable. I carefully
calibrated my 3 nanoVNA's (nanoVNA 2.8", nanoVNA H4, nanoVNA SAA-2N), each
50kHz to 300MHz. Then I recorded the values of the components at position 7
(capacitor) and posn. 8 (inductor) at increments over the frequency range.

Ed there are two versions of the RF demo board and at least 3 manufacturers. The test positions are different between the two. Photos of each attached. You can see that positions 7 and 8 on the NWDZ board are a capacitor and inductor respectively. However on the more commonly available DeepElec board 7 is a resistor and cap in series and 8 is an inductor and cap in series.

Are you using the NWDZ board and are you using the short, open and load on that board to calibrate?

Roger

Never........NEVER.......rely on an electrolytic as a bypass for RF
energy!!!!!! Use series resonance to your advantage. Chip, N6CA learned
that lesson from (deceased) Gary Frey, W6XJ, in the 1970's. The bypass
caps presented in his preamps are chosen to be self resonant at the
frequency of operation of each preamp. I've used the technique many times
over in home brewing. It's a well known fact among (most) design
engineers that tantalum capacitors are not much good above 500 kHz to a
couple of MHz. Most electrolytics are even worse. Go measure them on
your NANOs.

I just grabbed a 1000 ?F / 25 VDC cap from the parts bin and measured it on
a calibrated HP 8753C using the Smith Chart. Even at 1 MHz it measures 78
mΩ with a series reactance 78 nH. Sure, the DC portion is fine, but what
is 78 nH at 50 MHz?

X(L) = 2 x π x f x L = 6.28 x [50 E 6] x [78 E-9] = 24.5 ohms

Sure, the +j24.5 is non-dissipative, but does not make a very good bypass
even at low VHF frequencies.

Take a capacitor better suited as a bypass at HF, a 450 pF dip mica. Same
setup at 10 MHz: 0.1 ohms at 462 pF. It goes self resonant just above 39
MHz.

Which makes a better bypass at HF.

Dave - W?LEV

On Sun, Feb 14, 2021 at 10:14 PM Manfred Mornhinweg <manfred@...>
wrote:

And what's the best bypass cap? Well, a single, plain, cheap aluminium
electrolytic!

Attached is the impedance plot for a 47?F, 25V electrolytic cap, measured
with lead lengths compatible with mounting it snugly on a PCB. Their narrow
pin spacing helps a lot in keeping their ESL low. I kept the same scale to
make comparison easy.

YES, a single 47?F electrolytic is a much better bypass cap than a
parallel combination of two ceramic caps of different values! Even in the
low VHF range!

The problems with electrolytic caps is that their ESR rises with age, and
rises much faster if they run hot, or if they have to carry large ripple
current. So they can't be applied in every situation. But in situations
that are kind to them, they are the cheapest and easiest way to get an
excellent wideband bypass.

--
*Dave - W?LEV*
*Just Let Darwin Work*

That makes no sense whatsoever.

I have measured electrolytic capacitors with my nano and they are woefully bad at high frequencies.? Now that I have acquired a nanoVNA that can go down to 10 kHz I plan to do some testing to see if they are just as bad at that frequency.
Bob

Ed,

In a previous post I asked you which RF Demo board you were using. I took a look at both models that are being sold and from the photos it looks like one has a better layout of the cal loads for open, short and load. Layout and parts placement will affect the reference plane. Photo attached.

Roger

NWDZ board, like it says in the graphs. All calibrated on the same board with a single cable, as stated. And results were repeatable; I ran it several times. Are the board standards 100% accurate? Who knows? But the results were remarkably consistent over specific ranges.
--
Ed K9EK

On Sun, Feb 14, 2021 at 03:59 PM, Bob Albert wrote:

I have measured electrolytic capacitors with my nano and they are woefully
bad at high frequencies.? Now that I have acquired a nanoVNA that can go down
to 10 kHz I plan to do some testing to see if they are just as bad at that
frequency.
Bob

Bob,

I thought you might find this interesting. I took a small Siemens 10 uF 40V electrolytic and made some measurements on a DE-5000 RLC meter and compared them with the NanoVNA. At 10 kHz. and 100 kHz. The results were very close. Most manufacturers rate their electrolytics at 100 or 120 Hz. so these measurements are in the table below.

You can see on the plots that this one went into self resonance at 420 kHz which is low and probably due to the fact that I left the leads at 1 inch long.

Roger

And yet here we have two electrolytics in an RF circuit in a legendary piece of ham gear. I asked an actual rocket scientist about it and he didn't think it was anything unusual.

73

-Jim
NU0C

On Mon, 15 Feb 2021 00:55:06 +0100
"Dragan Milivojevic" <d.milivojevic@...> wrote:

That makes no sense whatsoever.

On Sun, 14 Feb 2021 at 23:14, Manfred Mornhinweg <manfred@...> wrote:

And what's the best bypass cap? Well, a single, plain, cheap aluminium
electrolytic!

Attached is the impedance plot for a 47?F, 25V electrolytic cap, measured
with lead lengths compatible with mounting it snugly on a PCB. Their narrow
pin spacing helps a lot in keeping their ESL low. I kept the same scale to
make comparison easy.

YES, a single 47?F electrolytic is a much better bypass cap than a
parallel combination of two ceramic caps of different values! Even in the
low VHF range!

The problems with electrolytic caps is that their ESR rises with age, and
rises much faster if they run hot, or if they have to carry large ripple
current. So they can't be applied in every situation. But in situations
that are kind to them, they are the cheapest and easiest way to get an
excellent wideband bypass.

The left hand one is bypassed with a .01 so that doesn't count.? I am puzzled by the other one; what's it supposed to do?

In parallel with a 10nF cap ...

Yeah, I remembered that about the one on the left after I sent the pic. The one on the right he called a "buzz kill".

73

-Jim
NU0C

On Mon, 15 Feb 2021 02:07:44 +0000 (UTC)
"Bob Albert via groups.io" <bob91343@...> wrote:

The left hand one is bypassed with a .01 so that doesn't count.? I am puzzled by the other one; what's it supposed to do?

Not the one on the right. See my previous post.

73

-Jim
NU0C

On Mon, 15 Feb 2021 03:14:37 +0100
"Dragan Milivojevic" <d.milivojevic@...> wrote:

In parallel with a 10nF cap ...

On Mon, 15 Feb 2021 at 03:02, Jim Shorney <jshorney@...> wrote:

And yet here we have two electrolytics in an RF circuit in a legendary
piece of ham gear. I asked an actual rocket scientist about it and he
didn't think it was anything unusual.

73

-Jim
NU0C

On Mon, 15 Feb 2021 00:55:06 +0100
"Dragan Milivojevic" <d.milivojevic@...> wrote:

That makes no sense whatsoever.

On Sun, 14 Feb 2021 at 23:14, Manfred Mornhinweg <manfred@...>

wrote:

And what's the best bypass cap? Well, a single, plain, cheap aluminium
electrolytic!

Attached is the impedance plot for a 47?F, 25V electrolytic cap,

measured

with lead lengths compatible with mounting it snugly on a PCB. Their

narrow

pin spacing helps a lot in keeping their ESL low. I kept the same

scale to

make comparison easy.

YES, a single 47?F electrolytic is a much better bypass cap than a
parallel combination of two ceramic caps of different values! Even in

the

low VHF range!

The problems with electrolytic caps is that their ESR rises with age,

and

rises much faster if they run hot, or if they have to carry large

ripple

current. So they can't be applied in every situation. But in situations
that are kind to them, they are the cheapest and easiest way to get an
excellent wideband bypass.

Forgot to ask, what's this legendary piece of equipment,
it has transistors so it can't be that good ?

Drake TR7/TR4310.

73

-Jim
NU0C

On Mon, 15 Feb 2021 03:31:07 +0100
"Dragan Milivojevic" <d.milivojevic@...> wrote:

Forgot to ask, what's this legendary piece of equipment,
it has transistors so it can't be that good ?

On Mon, 15 Feb 2021 at 03:27, Jim Shorney <jshorney@...> wrote:

Yeah, I remembered that about the one on the left after I sent the pic.
The one on the right he called a "buzz kill".

73

-Jim
NU0C

On Mon, 15 Feb 2021 02:07:44 +0000 (UTC)
"Bob Albert via groups.io" <bob91343@...> wrote:

The left hand one is bypassed with a .01 so that doesn't count. I am

puzzled by the other one; what's it supposed to do?

Dave,

it's a lot of fun to reply to you! You challenge me, and move me to measuring more things! So now I have to dissect your answer;

Never........NEVER.......rely on an electrolytic as a bypass for RF
energy!!!!!!

WHY? I accept such generalized statements only when they are delivered with generally valid fundamentation. The only reason I can see is that the ESR of an electrolytic capacitor is typically higher than that of a ceramic one. Thus, when bypassing is required only over a frequency range where a sufficiently small ceramic capacitor also provides low reactance, the ceramic is fine. But when good bypassing is needed, say, from 30kHz to 300MHz, what value of ceramic capacitor would you use? In such a case an electrolytic capacitor is required. Common wisdom says that it would be wise to parallel it with a small ceramic cap, but if you look at my measurement below, it turns out that an electrolytic alone can be plenty good enough - specially if it's an SMD.

Use series resonance to your advantage.

This is common practice in the microwave range, where the inductance of any part of practical size is too high for effective bypassing without resonance. But it's always narrow banded.

It's a well known fact among (most) design
engineers that tantalum capacitors are not much good above 500 kHz to a
couple of MHz. Most electrolytics are even worse. Go measure them on
your NANOs.

I did. The graphs are below. A plain run-of-the-mill SMD tantalum cap, 15?F, turns out having an impedance below 0.2? from 50kHz to 300MHz. What's bad about that? If indeed engineers know what you say, then they know wrong. They probably never measured it, and only ever believed in hearsay. Or took data measured long ago, on long-obsolete, giant size capacitors, that simply isn't applicable to modern, small size parts. Look at my RXZ curves below for that tantalum SMD cap.

I just grabbed a 1000 ?F / 25 VDC cap from the parts bin and measured it on
a calibrated HP 8753C using the Smith Chart. Even at 1 MHz it measures 78
mΩ with a series reactance 78 nH. Sure, the DC portion is fine, but what
is 78 nH at 50 MHz?

78nH suggests that it's a large, long, axial-lead capacitor. Of course you should NOT use that for RF bypassing! I just measured a modern radial-lead 1000?F 25V electrolytic, and got 6.8nH, more than 10 times better than yours! At that level, it's not much worse at 50MHz than any typical leaded ceramic cap. You just can't beat physics, and lead length costs inductance. Only SMDs get much better.

Take a capacitor better suited as a bypass at HF, a 450 pF dip mica.

WHAT?????? HF is 3 to 30MHz. 450pF has a reactance of 118? at 3MHz! Good luck with using that as a bypass!

Same setup at 10 MHz: 0.1 ohms at 462 pF.

That's its resistance, but its reactance at 10MHz is several tens of ohm, and thus it's pretty useless as a bypass. Except in high impedance circuitry.

I think that you need to get the basics straight...

Here are some measurements on candidate bypass capacitors, from 50kHz to 300MHz. First a typical small ceramic 100nF bypass cap, then a typical cheap 47?F 25V aluminium electrolytic, then a tantalum cap of the same rating, and then a 15?F 20V SMD tantalum cap. I kept the same scaling for all four graphs, for easy comparison. Judge yourself what's best, and do away with long-standing, unfounded prejudice!

Of course these graphs only show resistance, reactance, and impedance, not their ability to handle high currents, run in hot environments, and so on. In high power circuits the need to handle high current or heat might dictate the use of a capacitor that doesn't have the lowest impedance.

Very clearly these measurements run straight against the myth that electrolytic capacitors are useless at RF.

Just one more graph, as an addition: A 100nF 100V, 1206-size SMD multilayer ceramic cap. Above 20MHz the performance of the 100nF ceramic and the 15?F tantalum are very much the same, while below 20MHz the ceramic one gets progressively bad, while the tantalum one stays pretty good the low end of the frequency range measured.

Ergo: A tantalum electrolytic chip cap is a better, wider bandwidth bypass than a ceramic chip cap. From 20 to 300MHz there is no significant difference between them in bypassing performance, although I would expect the ceramic cap to handle more current over a longer time.

Forgot to ask, what's this legendary piece of equipment,
it has transistors so it can't be that good ?

Remove them! :-))

OK. I'm stupid and really don't know what I'm talking about. I spread
snake oil, saucery, witchcraft, and magic as applied to RF. Smith charts
are just disguised wiggie boards. And, of course, the earth is flat and
all celestial movements are determined by epicycles and epispheres. I
spent 10 years in RF design and the last 30 in EMC/RFI. Color me stupid,
dumb, incapable of handling DC Ohm's Law and don't know which end of the
soldering pen to grab.

I do not appreciate being attacked for my posts. I am working on data and
will post to this group.

Electrolytic, tantalums do NOT make good bypasses for high frequencies. I
proved that to myself decades ago in RF design and following in control of
EMC/RFI. Go build a preamp using only SMD 'electrolytics'. Control RF
emission of a ?P ringing at 3.6 GHz with only SMD 'electrolytics'. I am
taking data on that and will present it to this group. Please hold off on
flaming me further until that work is complete?

Dave - W?LEV

--
*Dave - W?LEV*
*Just Let Darwin Work*

On second thought, forget it. Those of us who have been there, done that
know better. I have a well outfitted RF lab covering to 21 GHz and know
how to use the equipment. I'm through replying to your posts. Go find
someone else to flame......

Reapectfully submetted:

Dave - W?LEV

On Mon, Feb 15, 2021 at 6:17 PM David Eckhardt <davearea51a@...>
wrote:

OK. I'm stupid and really don't know what I'm talking about. I spread
snake oil, saucery, witchcraft, and magic as applied to RF. Smith charts
are just disguised wiggie boards. And, of course, the earth is flat and
all celestial movements are determined by epicycles and epispheres. I
spent 10 years in RF design and the last 30 in EMC/RFI. Color me stupid,
dumb, incapable of handling DC Ohm's Law and don't know which end of the
soldering pen to grab.

I do not appreciate being attacked for my posts. I am working on data and
will post to this group.

Electrolytic, tantalums do NOT make good bypasses for high frequencies. I
proved that to myself decades ago in RF design and following in control of
EMC/RFI. Go build a preamp using only SMD 'electrolytics'. Control RF
emission of a ?P ringing at 3.6 GHz with only SMD 'electrolytics'. I am
taking data on that and will present it to this group. Please hold off on
flaming me further until that work is complete?

Dave - W?LEV

On Mon, Feb 15, 2021 at 2:43 AM Jim Shorney <jshorney@...>
wrote:

Drake TR7/TR4310.

73

-Jim
NU0C

On Mon, 15 Feb 2021 03:31:07 +0100
"Dragan Milivojevic" <d.milivojevic@...> wrote:

Forgot to ask, what's this legendary piece of equipment,
it has transistors so it can't be that good ?

On Mon, 15 Feb 2021 at 03:27, Jim Shorney <jshorney@...>

wrote:

Yeah, I remembered that about the one on the left after I sent the

pic.

The one on the right he called a "buzz kill".

73

-Jim
NU0C

On Mon, 15 Feb 2021 02:07:44 +0000 (UTC)
"Bob Albert via groups.io" <bob91343@...> wrote:

The left hand one is bypassed with a .01 so that doesn't count. I

am

puzzled by the other one; what's it supposed to do?

--
*Dave - W?LEV*
*Just Let Darwin Work*

--
*Dave - W?LEV*
*Just Let Darwin Work*

By the way, Ed is very well known in the VHF-UHF community. He has designed
and built some really cool solid-state amps for 144, 222 amd 432 MHz in the
200-300 watt range.

Zack W9SZ